1. Field of the Invention
This invention relates to a device for establishing a datum position from an object having dimensional variations within a tolerance range and holding that datum while work is being performed on the object that generated the datum position. More particularly, the invention relates to a method and apparatus for interaction with a frame-like member, such as an automobile body wherein pre-established variable reference surfaces are detected by the apparatus to establish a datum position. The apparatus then references the datum position and accomplishes work on the automobile body in relationship to the datum position.
2. Description of the Prior Art
An apparatus for assembling a door on an automobile body is set forth in U.S. Pat. No. 4,589,199, which issued May 20, 1986, in the name of Keizaburo Ohtaki et al. In this patent, a set jig is supported on a shift table that is positioned adjacent to an automobile assembly line that can accommodate automobile components, such as the incomplete body structure. The apparatus described in U.S. Pat. No. 4,589,199 is dedicated to the installation of automobile door assemblies to predetermined attachment points that have already been established on the automobile body framework. The set jig can move from front to rear along the automobile body structure. The movement is further enhanced by a three-dimensional right angled coordinate type robot mechanism which is movable with respect to the width and length, as well as the height of the automobile body structure. The robot mechanism is provided on a shift table that has a first movable frame movable in the automobile body length direction, a second movable frame which is provided on the first movable frame and which is movable in the automobile body width direction, and a third movable frame which is provided on the second movable frame and which is movable in the automobile body height direction.
The robot mechanism additionally can support a door assembly and move it into the proper assembly position on the automobile body. In order to compensate for variations in the location of the door attachment points on the automobile body, a probe is moved into engagement with the door attachment point of the automobile body. If the probe detects any deviation in the location of the door attachment point as compared to where it should be, the deviation is communicated through electrical means to the robot mechanism so that it can compensate as it moves the door into an attachment position.
Thus, it can be realized that while the above described apparatus permits automotive body deviations to be taken into account during the assembly of a door, the deviation from the normal attachment point must be first ascertained; the, after the probe has been moved into and out of engagement with the automotive body, the actual task of swinging the door panel into an acceptable attachment location can be undertaken. Then, too, a normal reference point must be established on the assembly line, the automobile body, or both so the probe can successively calculate the deviation, if any, and communicate such deviation to the three axis positioning portion of the apparatus.
In U.S. Pat. No. 4,086,522, which issued Apr. 25, 1978, in the name of Joseph F. Engelberger et al, a programmable manipulator is described and illustrated. The apparatus set forth in this patent is useful in performing welding functions during the assembly of an automobile body frame. The manipulator relies on a complex electrical program with memory retention capacity to store a series of statically-taught work positions that are acquired from a stationary workpiece.
The computer stored information is then used as a comparison base when the manipulator apparatus is utilized on a moving automobile body assembly line.
Since the manipulator apparatus of U.S. Pat. No. 4,086,522 performs its motion in accordance with an internally retained memory proram, it is difficult to control precisely the location of the tool being held by the manipulator end arm. Variations in automobile bodies is a fact and once the body dimensions move outside the range of the pre-recorded deviations, time must be taken to reprogram the memory of the manipulator apparatus so that work on the moving conveyor line can resume. Such a recalibration procedure is costly and time consuming in that the conveyor line must be stopped while the memory means is being reprogrammed.